Electrophotographic photosensitive member containing disazo compound

ABSTRACT

An electrophotographic photosensitive member comprises a photosensitive layer on a substrate, said photosensitive layer comprising a disazo pigment represented by the formula (1).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an electrophotographic photosensitive memberutilizing a novel electrophotographic photosensitive material, moreparticularly to an electrophotographic photosensitive memberincorporating a disazo pigment having a specific molecular structure inthe photosensitive layer.

2. Related Background Art

Pigments and dyes exhibiting photoconductivity have been heretoforereported in a large number of literatures. For example, there is areport about photoconductivity of phthalocyanine pigments in "RCAReview" Vol. 23, p. 413-419, September, 1962, and electrophotographicphotosensitive members employing the phthalocyanine pigments aredisclosed in U.S. Pat. Nos. 3,397,086 and 3,816,118. Otherwise, asorganic semiconductors to be used for electrophotographic photosensitivemembers, there may be included, for example, pyrilium dyes disclosed inU.S. Pat. Nos. 4,315,983 and 4,327,169, and "Research Disclosure" 20517,May, 1981; squaric acid methine dyes disclosed in U.S. Pat. No.3,824,099; and disazo pigments disclosed in U.S. Pat. Nos. 3,898,084 and4,251,613.

Such organic semiconductors can be synthetized more readily as comparedto inorganic semiconductors, and also they can be synthesized as thecompounds having photoconductivity to the light of the requiredwavelength region. An electrophotographic photosensitive member having acoating of such an organic semiconductor formed on an electroconductivesupport has the advantage of improved color sensitivity, but only a feware satisfactory for practical purposes with respect to sensitivity anddurability.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a novel photoconductivematerial.

Another object of the present invention is to provide anelectrophotographic photosensitive member which can be used in all ofthe existing electrophotographic processes and is provided withexcellent practical sensitivity and durability having stable potentialcharacteristics during repeated uses.

In accordance with the present invention, there is provided anelectrophotographic photosensitive member having a photosensitive layeron an electroconductive substrate, said photosensitive layer comprisinga disazo pigment represented by the formula (1): ##STR1## wherein R₁, R₁', R₂, R ₂ ', and A are defined below.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the above formula (1), R₁, R₁ ', R₂ and R₂ ' represent hydrogen,halogen, nitro, cyano or; alkyl, aralkyl, alkoxy or aryl group, thelatter four groups of which may have a substituent, A represents acoupler residue having a phenolic OH group, and B represents hydrogen ornitroso group.

As the groups defined by R₁, R₁ ', R₂ and R₂ ', the alkyl group mayinclude, for example, methyl, ethyl, propyl, and the like; the aralkylgroup, for example, benzyl, phenethyl, naphthylmethyl and the like; thearyl group phenyl, diphenyl, naphthyl and the like; the alkoxy group,for example, methoxy, ethoxy and the like; the halogen fluorine,chlorine, bromine and iodine; and further cyano group and nitro groupare included.

Examples of the substituents with which R₁, R₁ ', R₂ and R₂ ' may besubstituted may include alkyl groups such as methyl, ethyl, propyl andthe like; aralkyl groups such as benzyl, phenethyl, naphthylmethyl andthe like; aromatic groups such as phenyl, naphthyl, anthranyl and thelike; alkoxy groups such as methoxy, ethoxy and the like; halogen atomssuch as fluorine, chlorine, bromine, iodine; and further cyano group andnitro group.

Further, the coupler residue having a phenolic OH group of A in theformula (1) may include those of the following formulae (2) to (8):##STR2## wherein X represents a residue to be fused with a benzene ringto form a polycyclic aromatic ring of anthracene ring, or a heterocyclicring, all of which may have a substituent; R₃ and R₄ represent hydrogen,alkyl, aryalkyl, aryl or heterocyclic ring, the latter four groups ofwhich have a substituent, or taken together represent a residue to forma cyclic amino group together with the nitrogen atom; R₅ and R₆ eachrepresent alkyl, aralkyl, aryl, all of which may have a substituent; Yrepresents a divalent aromatic hydrocarbon group or forms a divalentheterocyclic group together with the nitrogen atoms; Z represents aresidue to be fused with a benzene ring to form a polycyclic aromaticring or heterocyclic ring; R₇ and R₈ represent hydrogen, aryl orheterocyclic group, the latter two of which may have a substituent or aresidue which forms a 5- to 6-membered ring together with the centercarbon atom, which 5- to 6-membered ring may have a fused aromatic ring;R₉ and R₁₀ represent hydrogen, alkyl, aralkyl, aryl or heterocyclicgroup, the latter four of which may have a substituent.

The above polycyclic aromatic ring to be formed by fusion of X with thebenzene ring is anthracene, and examples of the above heterocyclic ringto be formed by such fusion of X may include carbazole, benzcarbazole,dibenzofuran, benzonaphthofuran, diphenylenesulfide and others. Thesemay be substituted with substituents as mentioned above. The fused ringto be formed by fusion of X with benzene ring may desirably beanthracene, benzcarbazole or carbazole. In the case of R₃ and the R₄,the alkyl may be exemplified by methyl, ethyl, propyl, butyl and thelike; the aralkyl by benzyl, phenethyl, naphthylmethyl and the like; thearyl by phenyl, diphenyl, naphthyl, anthryl and the like. Particularly,it is preferable to use a compound having a structure in which R₃ ishydrogen and R₄ is a phenyl group having an electron attracting groupsuch as halogen, nitro, cyano, trifluoromethyl and the like, or an alkylgroup such as methyl, ethyl, butyl and the like at the o-position.Examples of the heterocyclic ring include carbazole, dibenzofuran,benzimidazolone, benzthiazole, thiazole, pyridine and the like.

Typical examples of R₅ and R₆ may include the same as mentioned abovefor R₃ and R₄. These can also be substituted with the substituents asmentioned above. Further, R₃ to R₆ may be substituted with othersubstituents, including alkoxy groups such as methoxy, ethoxy, propoxy,etc.; halogens such as fluorine, chlorine, bromine, iodine, etc.; nitro;cyano; substituted amino group such as dimethylamino, diethylamino,dibenzylamino, diphenylamino, etc.

In the definition of Y, the divalent aromatic hydrocarbon group may be,for example, a monocyclic aromatic hydrocarbon group such aso-phenylene, or a fused polycyclic aromatic hydrocarbon group such aso-naphthylene, perinaphthylene, 1,2-anthrylene, 9,10-phenanthrylene andthe like. Examples of the divalent heterocyclic ring formed togetherwith nitrogen atom may include 5- to 6-membered divalent groups such as3,4-pyrozolediyl, 2,3-pyridinediyl, 4,5-pyrimidinediyl,6,7-indazolediyl, 5,6-benziimidazolediyl, 6,7-quinolinediyl group, etc.

The aryl group or the heterocyclic group of R₇ and R₈ may be examplifiedby phenyl, naphthyl, anthryl, pyrenyl, etc.; pyridiyl, thienyl, furyl,carbazolyl, etc. These may also be substituted with the substituents asmentioned above.

As the substituents on the aryl group and the heterocyclic grouprepresented by R₇ and R₈, there may be included halogens such asfluorine, chlorine, bromine, iodine, etc.; alkyl groups such as methyl,ethyl, propyl, butyl, etc.; alkoxy groups such as methoxy, ethoxy,propoxy, butoxy, etc.; nitro; cyano; substituted amino groups such asdimethylamino, diethylamino, dipropylamino, dibenzylamino,diphenylamino, morpholino, piperidino, pyrrolidino, etc. Also, R₇ and R₈may represent a residue forming a 5- to 6-membered ring together withthe center carbon atom, and the 5- to 6-membered ring may also have afused aromatic ring. The examples may include groups such ascyclopentylidene, cyclohexylidene, 9-fluorenylidene, 9-xanthenylidene,etc.

R₉ and R₁₀ in the formula (8) represent hydrogen or an optionallysubstituted: alkyl group (e.g. methyl, ethyl, propyl, butyl), aralkylgroup (e.g. benzyl, phenethyl, naphthylmethyl), aryl group (e.g. phenyl,naphthyl, anthryl, diphenyl) or heterocyclic group (e.g. carbazole,dibenzofuran, benzimidazolone, benzthiazole, thiazole, pyridene).Examples of the substituents on the alkyl, aralkyl, aryl or heterocyclicgroups represented by R₉ and R₁₀ may include halogens such as fluorine,chlorine, bromine, iodine, etc.; alkyl groups such as methyl, ethyl,propyl, butyl, etc.; alkoxy groups such as methoxy, ethoxy, propoxy,butoxy, etc.; nitro; cyano; substituted amino groups such asdimethylamino, dipropylamino, dibenzylamino, diphenylamino, morpholino,piperidino, pyrrolidino and the like.

Z in the formulas (7) and (8) represents a residue which is fused withbenzene ring to form a polycyclic aromatic ring or a heterocyclic ring.Examples of the polycyclic aromatic ring formed by the fusion of Z mayinclude naphthalene, and examples of the heterocyclic ring formed by thefusion of Z may include anthracene, carbazole, benzcarbazole,benzofuran, benzonaphthofuran, diphenylsulfide, etc. The ring to which Xis bonded may more desirably be an anthracene ring, benzcarbazole ringor carbazole ring. Particularly, benzcarbazole ring has a remarkableeffect of elongating the spectral sensitive region to longer wavelengthregion and is therefore preferably used for preparation of aphotosensitive member having high sensitivity to the semiconductor laserregion.

The disazo pigments of the present invention can be further improved inthe sensitivity by attachment of hydrogen or nitroso group to thenitrogen atom of the diarylamine skeleton and combination with thespecific coupler residue. Thus, high sensitivity can be achieved, andtherefore application for high speed copying machine, laser beamprinter, LED printer and liquid crystal printer is rendered possible.Further, it is also possible to obtain a beautiful image stably, becausestable potential can be ensured without dependence on the history of thephotosensitive member.

Examples of disazo pigment of the general formula (1) wherein B ishydrogen: ##STR3##

Examples of disazo pigment of the general formula (1) wherein B isnitroso group: ##STR4##

These disazo pigments can be used either singly or as a combination oftwo or more pigments.

These pigments can be prepared easily by, for example, subjecting adiamine having a secondary amine represented by the formula: ##STR5##wherein R₁, R₁ ', R₂, R₂ ' and B have the same meanings as the symbolsin the formula (1), to tetrazotization in the ordinary manner, thencarrying out aqueous system coupling of the corresponding coupler in thepresence of an alkali, or isolating once a tetrazonium salt of the abovediamine in the form of borofluoride or zinc chloride double salt withthe tetrazonium salt of the above diamines before coupling with acoupler in an appropriate solvent such as N,N-dimethylformamide,dimethyl sulfoxide, etc. in the presence of an alkali.

In the following, a typical example of synthesis of the disazo pigmentto be used in the present invention is shown.

SYNTHETIC EXAMPLE 1 [Synthesis of the Above Exemplary Disazo Pigment No.1-(1)]

A 500 ml beaker was charged with 80 ml of water and 16.6 ml (0.19 mole)of conc. hydrochloric acid and, while cooling on an ice-water bath, 5.7g (0.029 mole) of an amine: ##STR6## was added thereto under stirringand the liquid temperature was maintained at 3° C. Next, a solution of4.1 g (0.060 mole) of sodium nitrite dissolved in 7 ml of water wasadded dropwise over 10 minutes while controlling the liquid temperatureto the range of 3° to 10° C., and the mixture was stirred at the sametemperature for additional 30 minutes after completion of the dropwiseaddition. The reaction mixture was filtered with addition of carbon toobtain a tetrazotized mixture.

As the next step, a 2 liter beaker was charged with 700 ml ofdimethylformamide and 53.6 g (0.53 mole) of triethylamine was added,followed by addition of 19.1 g (0.061 mole) of3-hydroxy-2-anthracenecarboxylic acid anilide to be dissolved therein.

The resultant coupler solution was cooled to 6° C. and, whilecontrolling the liquid temperature at 6° to 10° C., the abovetetrazotized mixture was added dropwise under stirring over 30 minutes,and then stirred at room temperature for 2 hours, followed further byleaving to stand overnight. The reaction mixture was filtered, washedwith water and filtered to obtain 21.3 g (as solid) of a crude pigmentas water paste. Then, by use of 400 ml of N,N-dimethylformamide,stirring and filtration were repeated four times at room temperature.Then, after repeating stirring and filtration twice, respectively, with400 ml of methyl ethyl ketone, followed by drying under reduced pressureat room temperature, 20.9 g of a purified pigment was obtained. Theyield was 85.0%. m.p. >250°.

    ______________________________________                                        Elemental analysis                                                                             Calcd. (%)                                                                              Found (%)                                          ______________________________________                                        C                76.50     76.42                                              H                4.40      4.37                                               N                11.56     11.62                                              ______________________________________                                    

SYNTHETIC EXAMPLE 2 [Synthesis of the Above Exemplary Disazo Pigment No.2-(1)]

A 500 ml beaker was charged with 80 ml of water and 16.6 ml (0.19 mole)of conc. hydrochloric acid and, while cooling on an ice-water bath, 5.7g (0.029 mole) of an amine: ##STR7## was added thereto under stirringand the liquid temperature was maintained at 3° C. Next, a solution of6.2 g (0.090 mole) of sodium nitrite dissolved in 7 ml of water wasadded dropwise over 10 minutes while controlling the liquid temperatureto the range of 3° to 10° C., and the mixture was stirred at the sametemperature for additional 30 minutes after completion of the dropwiseaddition. The reaction mixture was filtered with addition of carbon toobtain a tetrazotized mixture.

As the next step, a 2 liter beaker was charged with 700 ml ofdimethylformamide and 53.6 g (0.53 mole) of triethylamine was added,followed by addition of 19.1 g (0.061 mole) of3-hydroxy-2-anthracenecarboxylic acid anilide to be dissolved therein.

The resultant coupler solution was cooled to 6° C. and, whilecontrolling the liquid temperature at 6° to 10° C., the abovetetrazotized mixture was added dropwise under stirring over 30 minutes,and then stirred at room temperature for 2 hours, followed further byleaving to stand overnight. The reaction mixture was filtered, washedwith water and filtered to obtain 22.8 g (as solid) of a crude pigmentas water paste.

Then, by use of 400 ml of N,N-dimethylformamide, stirring and filtrationwere repeated four times at room temperature. Then, after repeatingstirring and filtration twice, respectively, with 400 ml of methyl ethylketone, followed by drying under reduced pressure at room temperature,21.5 g of a purified pigment was obtained. The yield was 84.6%. m.p.>250°.

    ______________________________________                                        Elemental analysis                                                                             Calcd. (%)                                                                              Found (%)                                          ______________________________________                                        C                73.97     73.95                                              H                4.11      4.10                                               N                12.79     12.77                                              ______________________________________                                    

Having described above about the synthetic method of typical pigments,other disazo pigments represented by the formula (1) can also similarlybe synthesized.

The coating containing the disazo pigment as described above exhibitsphotoconductivity and can be used for the photosensitive layer in theelectrophotographic photosensitive member as described below.

That is, according to a typical embodiment of the present invention, anelectrophotographic photosensitive member can be prepared by forming acoating of a disazo pigment as described above by the vacuum vapordeposition method on an electroconductive substrate, or by forming acoating of the disazo pigment dispersed in a suitable binder.

According to a preferable example of the present invention, thephotosensitive layer of the electrophotographic member is separated infunction into the charge generation layer and the charge transportlayer, and the photoconductive coating as described above can be appliedas the charge generation layer of the electrophotographic photosensitivemember.

The charge generation layer contains a compound exhibitingphotoconductivity as mentioned above in an amount as much as possible inorder to obtain sufficient light absorbance, and is preferably made of athin film, having a thickness of, for example, 5μ or less, preferably0.01 to 1μ, in order to make the flight length of the charge carriersgenerated. This is attributable to the fact that most of the quantity ofincident light is absorbed by the charge generation layer to generatemuch charge carriers and further that the charge carriers generated arerequired to be injected into the charge transport layer withoutdeactivation by recombination or trap.

The charge generation layer can be formed by dispersing the abovecompound in a suitable binder and applying the dispersion on the abovesubstrate by way of coating, and it can also be obtained by forming avapor deposited film by means of a vacuum vapor deposition device. Thebinder which can be used in formation of the charge generation layer byway of coating can be selected from a wide variety of insulating resins,and also from organic photoconductive polymers such aspoly-N-vinylcarbazole, polyvinylanthracene, polyvinylpyrene, etc.Preferably, there may be employed insulating resins such as polyvinylbutyral, polyalylate (e.g. condensed polymer of binsphenol A andphthalic acid), polycarbonate, polyester, phenoxy resin, polyvinylacetate, acrylic resin, polyacrylamide resin, polyamide, polyvinylpyridine, cellulose type resin, urethane resin, epoxy resin, casein,polyvinyl alcohol, polyvinyl pyrrolidone, etc. The amount of the resincontained in the charge generation layer may suitably be 80% by weightor less, preferably 40% by weight or less.

The solvent used for dissolving these resins differs depending on theresin employed and is also preferably selected from those which do notdissolve the charge transport layer and the subbing layer as describedbelow. Typical examples of organic solvents may include alcohols such asmethanol, ethanol, isopropanol and the like; ketones such as acetone,methyl ethyl ketone, cyclohexanone and the like; amides such asN,N-dimethylformamide, N,N-dimethylacetamide and the like; sulfoxidessuch as dimethyl sulfoxide and the like; ethers such as tetrahydrofuran,dioxane, ethylene glycol monomethyl ether and the like; esters such asmethyl acetate, ethyl acetate and the like; aliphatic halogenatedhydrocarbons such as chloroform, methylene chloride, dichloroethylene,carbon tetrachloride, trichloroethylene and the like; aromatics such asbenzene, toluene, xylene, ligroin, monochlorobenzene, dichlorobenzeneand the like; and so on.

Coating can be practiced by dip coating, spray coating, spinner coating,bead coating, Meyer bar coating, blade coating, roller coating, curtaincoating, etc. Drying is preferably conducted by way of finger touchdrying at room temperatures, followed by heating drying. Heating dryingcan be conducted at a temperature of 30° C. to 200° C., for 5 minutes to2 hours, either under stationary state or under air blowing.

The charge transport layer is electrically connected to the chargegeneration layer as described above, has the function of receivingcharge carriers injected from the charge generation layer in thepresence of an electrical field and transporting these charge carriersto the surface. The charge transport layer may be laminated either onthe charge generation layer or beneath thereof. When the chargetransport layer is formed on the charge generation layer, the substancefor transporting the charge carriers in the charge transport layer(hereinafter referred to merely as charge transport substance) ispreferably substantially non-sensitive to the wavelength region of theelectromagnetic wave to which the cahrge generation layer as describedabove is sensitive. The "electromagnetic wave" as herein mentioned isinclusive of "light rays" in a broad sense, including γ-ray, X-ray,UV-ray, visible ray, near IR-ray, IR-ray and far IR-ray. When thelight-sensitive wavelength region of the charge transport layercoincides with or overlaps that of the charge generation layer, thecharge carriers generated in both layers will trap each other, to resultin lowering of sensitivity.

The charge transport material may include electron transport substancesand positive hole transport substances. Examples of electron transportsubstances are electron attracting substances such as chloranil,bromoanil, tetracyanoethylene, tetracyanoquinodimethane, fluorenonessuch as 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone and2,4,7-trinitro-9-dicyanomethylenefluorenone and the like;2,4,5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone, etc. or polymersformed from these electron attracting substances.

Examples of positive hole transport substances include pyrene,N-ethylcarbazole, N-isoproylcarbazole,N-methyl-N-phenylhydrazino-3-methylidene-9-ethylcarbazole,N,N-diphenylhydrazino-3-methylidene-9-ethylcarbazole,N,N-diphenylhydrazino-3-methylidene-10-ethylphenothiazine,N,N-diphenylhydrazino-3-methylidene-10-ethylphenoxazine, hydrazones suchas p-diethylaminobenzaldehyde-N,N-diphenylhydrazone,p-diethylaminobenzaldehyde-N-α-naphthyl-N-phenylhydrazone,p-pyrrolidinobenzaldehyde-N,N-diphenylhydrazone,1,3,3-trimethylindolenine-ω-aldehyde-N,N-diphenylhydrazone,p-diethylbenzaldehyde-3-methylbenzthiazolinone-2-hydrozone and the like,2,5-bis(p-diethylaminophenyl)-1,3,4-oxadiazole, pyrazolines such as1-phenyl-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline,1-[quinolyl(2)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)-pyrazoline,1-[pyridyl(2)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline,1-[6-methoxy-pyridyl(2)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline,1-[pyridyl(3)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline,1-[lepidyl(2)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline,1-[pyridyl(2)]-3-(p-diethylaminostyryl)-4-methyl-5-(p-diethylaminophenyl)pyrazoline,1-[pyridyl-(2)]-3-(α-methyl-p-diethylaminostyryl)-5-(p-diethylaminophenyl)-pyrazoline,1-phenyl-3-(p-diethylaminostyryl)-4-methyl-5-(p-diethylaminophenyl)pyrazoline,1-phenyl-3-(α-benzyl-p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline,spiropyrazoline and the like, oxazole compounds such as2-(p-diethylaminostyryl)-6-diethylaminobenzoxazole,2-(p-diethylaminophenyl)-4-(p-dimethylaminophenyl)-5-(2-chlorophenyl)oxazoleand the like, thiazole compounds such as2-(p-diethylaminostyryl)-6-diethylaminobenzothiazole and the like,triarylmethane compounds such asbis(4-diethylamino-2-methylphenyl)phenylmethane and the like, polyarylalkanes such as 1,1-bis(4-N,N-diethylamino-2-methylphenyl)heptane,1,1,2,2-tetrakis(4-N,N-dimethylamino-2-methylphenyl)ethane and the like,triphenylamine, poly-N-vinylcarbazole, polyvinylpyrene,polyvinylanthracene, polyvinylacridine, poly-9-vinylphenylanthracene,pyrene-formaldehyde resin, ethylcarbazole-formaldehyde resin, etc.

Other than these organic charge transport substances, inorganicmaterials such as selenium, selenium-tellurium amorphous silicon,cadmium sulfide may also be used.

Further, these charge transport substances can be used either singly oras a combination of two or more compounds.

When the charge transport substance has no film forming property,coating can be formed by selection of a suitable binder. The resin whichcan be used as the binder may include, for example, insulating resinssuch as acrylic resin, polyalylate, polyester, polycarbonate,polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadienecopolymer, polyvinyl butyral, polyvinyl formal, polysulfone,polyacrylamide, polyamide, chlorinated rubber and the like, or organicphotoconductive polymers such as poly-N-vinylcarbazole,polyvinylanthracene, polyvinylpyrene, etc.

The charge transport layer cannot be made thicker than need be, becausethere is the limit of thickness which can transport charge carriers. Thethickness is generally 5 to 30μ, preferably within the range from 8 to20μ. In forming the charge transport layer by coating, a suitablecoating method as described above can be employed.

The photosensitive layer comprising such a laminated structure of chargegeneration layer and charge transport layer is provided on a substratehaving an electroconductive layer. The substrate having anelectroconductive layer may include those in which the substrate itselfhas electroconductivity, such as aluminum, aluminum alloys, copper,zinc, stainless steel, vanadium, molybdenum, chromium, titanium, nickel,indium, gold, platinum, etc., or otherwise plastics (e.g. polyethylene,polypropylene, polyvinyl chloride, polyethylene terephthalate, acrylicresin, polyfluoroethylene, etc.) having a layer of aluminum, aluminumalloys, indium oxide, tin oxide, indium oxide-tin oxide alloys, etc.coated by the vaccum vapor deposition method thereon, substrates ofplastics or the above electrocondutive substrate coated withelectroconductive particles (e.g. aluminum powder, tin oxide, zincoxide, titanium oxide, carbon black, silver particles, etc.) in asuitable binder, substrates of plastics or papers impregnated withelectroconductive particles, or plastics having electroconductivepolymers, etc.

Between the electroconductive layer and the photosensitive layer, asubbing layer having the barrier function and the adhesive function canalso be provided. The subbing layer can be formed of casein, polyvinylalcohol, nitrocellulose, ethylene-acrylic acid copolymer, poliamide(nylon 6, nylon 66, nylon 610, copolymerized nylon, alkoxymethylatednylon), polyurethane, gelatin, aluminum oxide, etc.

The film thickness of the subbing layer may be suitably 0.1 to 5μ,preferably 0.5 to 3μ.

In the case of using a photosensitive member having an electroconductivelayer, a charge generation layer and a charge transport layer in theorder stated, when the charge transport substance comprises an electrontransportable substance, the surface of the charge transport layer isrequired to be changed positively. When exposure is effected aftercharging, the electrons generated in the charge generation layer at theexposed portion are injected into the charge transport layer, andthereafter reach the surface where the positive charges are neutralizedto cause decay of the surface potential, whereby electrostatic contrastcan be created between the exposed and the unexposed portions. Theelectrostatic latent image thus formed is developed with a negativelychargeable toner to give a visible image. This can be directly fixed, ordevelped after transfer of the toner image onto a paper or a plasticfilm, followed by fixing.

It is also possible to employ the method in which the electrostaticlatent image is transferred onto an insulating layer such as transferpaper and then developed, followed by fixing. The developing agent, thedeveloping method and the fixing method used may be any of those knownin the art, and will not be limited to particular ones.

On the other hand, when the charge transport substance comprises apositive hole transport substance, the charge transport layer surface isrequired to be negative charged. When exposure is effected aftercharging, the positive holes generated in the charge generation layer atthe exposed portion are injected into the charge transport layer andthereafter reach the surface to neutralize the negative charges, wherebydecay of the surface potential is caused to create an electrostaticcontrast between the exposed and the unexposed portions. Duringdevelopment, it is necessary to use a positively chargeable toner, ascontrary to the case of using an electron transportable substance.

In the case of using a photosensitive member having an electroconductivelayer, a charge transport layer and a charge generation layer in theorder stated, when the charge transport substance comprises an electrontransportable substance, the surface of the charge generation layer isrequired to be charged negatively. When exposure is effected aftercharging, the electrons generated in the charge generation layer at theexposed portion are injected into the charge transport layer, andthereafter reach the substrate. On the other hand, the positive holesgenerated in the charge generation layer reach the surface to causedecay of the surface potential, whereby electrostatic contrast iscreated between the exposed and unexposed portions. the electrostaticlatent image thus formed is developed with a positively chargeable tonerto give a visible image. This can be directly fixed or developed aftertransfer of the toner image onto a paper or a plastic film, followed byfixing. It is also possible to employ the method in which theelectrostatic latent image is transferred onto an insulating layer oftransfer paper and then developed, followed by fixing. The developingagent, the developing method and the fixing method used may be any ofthose known in the art, and will not be limited to particular ones.

On the other hand, when the charge generation layer comprises a positivehole transport substance, the charge generation layer surface isrequired to be positively charged. When exposure is effected aftercharging, the positive holes generated in the charge generation layer atthe exposed portion are injected into the charge transport layer andthereafter reach the substrate. On the other hand, electrons generatedin the charge generation layer reach the surface to cause decay of thesurface potential, whereby an electrostatic contrast is created betweenthe exposed and the unexposed portions. During development, it isnecessary to use a negatively chargeable toner, as contrary to the caseof using an electron transportable substance.

According to another embodiment of the present invention, aphotosensitive coating can be formed incorporating a disazo pigment asdescribed above as the sensitizer for organic photoconductive substancesas mentioned above such as hydrazones, pyrazolines, oxazoles, thiazoles,triarylmethanes, polyarylalkanes, triphenylamine,poly-N-vinylcarbazoles, etc. or inorganic photoconductive substancessuch as zinc oxide, cadmium sulfide, selenium, etc. The photosensitivecoating can be formed by way of coating of these photoconductivesubstances and the disazo pigment as described above together with abinder.

As still another embodiment of the present invention, there may beemployed an electrophotographic photosensitive member incorporating thedisazo pigment as described above together with the charge transportsubstance in the same layer. In this case, other than the chargetransport substance as described above, charge transfer complexcompounds comprising poly-N-vinylcarbazole and trinitrofluorenone can beused. The electrophotographic photosensitive member according to thisembodiment can be prepared by dispersing the above-mentioned disazopigment and the charge transfer complex compounds in a polyestersolution dissolved in tetrahydrofuran, followed by coating formation.

In any of the photosensitive members, the pigment used is at least onekind of pigment selected from the disazo pigments represented by theformula (1) and its crystal form may be either amorphous or crystalline.If desired, pigments with different light absorption can be used incombination to enhance the sensitivity of the photosensitive member, ortwo or more kinds of the disazo pigments represented by the formula (1)can be combined for the purpose of obtaining a panchromaticphotosensitive member, etc. Further, it is also possible to use chargegeneration substances selected from known dyes and pigments incombination with the disazo pigments.

The electrophotographic photosensitive member of the present inventioncan be utilized not only for electrophotographic copying machine butalso widely for electrophotography utilizing fields such as laserprinter, CRT printer, LED printer, liquid crystal printer, laserprinting plate, etc.

The present invention is described by referring to the followingExamples.

EXAMPLES 1--1 to 1-40

An aluminum plate was coated with an aqueous ammoniacal solution ofcasein (casein 11.2%, ammonia water 1 g, water 222 ml) by a Meyer bar toa film thickness after drying of 1.0μ, followed by drying.

Next, 5 g of the above exemplary disazo pigment No. 1--1 was added intoa solution of 2 g of a butyral resin (degree of butylation, 63 mole %)dissolved in 95 ml of ethanol and dispersed in a sand mill for 2 hours.The dispersion was applied by a Meyer bar on the casein layer previouslyformed to a film thickness after drying of 0.5μ, followed by drying, toform a charge generation layer. Subsequently, 5 g of a hydrazonecompound of the following formula: ##STR8## and 5 g of a polymethylmethacrylate resin (number average molecular weight: 100,000) weredissolved in 70 ml of benzene, and the resultant solution was applied bya Meyer bar on the charge generation layer to a film thickness afterdrying of 12μ, followed by drying, to form a charge transport layer.Thus, a photosensitive member of Example 1--1 was prepared. According toentirely the same procedure except for using the exemplary pigmentsshown in Table 1 in place of the disazo pigment No. 1--1, photosensitivemembers corresponding to Examples 1-2 to 1-40 were prepared.

The electrophotographic photosensitive members thus prepared weresubjected to corona charging at ⊖ 5 kV according to the static system bymeans of an electrostatic copying paper testing device Model SP-428produced by Kawaguchi Denki K. K., maintained in a dark place for onesecond and thereafter exposed at a illumination intensity of 2 lux forexamination of charging characteristics.

As the charging characteristics, the surface potential (Vo) and theexposure quantity necessary for decaying the potential when subjected todark decay for one second to 1/2 (E_(1/2)) were measured. The resultsare shown in Table 1--1.

                  TABLE 1-1                                                       ______________________________________                                                 Exemplary disazo                                                     Example  pigment No.    Vo (-V)  E.sub.1/2  (l · s)                  ______________________________________                                        1-1      1-1            560      4.0                                          1-2      1-2            600      3.2                                          1-3      1-3            580      2.9                                          1-4      1-4            570      3.0                                          1-5      1-5            600      2.6                                          1-6      1-6            580      2.8                                          1-7      1-7            600      2.4                                          1-8      1-8            610      3.3                                          1-9      1-9            600      2.6                                          1-10     1-10           620      2.6                                          1-11     1-11           610      2.7                                          1-12     1-12           590      2.9                                          1-13     1-13           590      4.3                                          1-14     1-14           610      4.1                                          1-15     1-15           570      3.2                                          1-16     1-16           570      2.9                                          1-17     1-18           600      2.6                                          1-18     1-19           590      2.4                                          1-19     1-20           570      3.8                                          1-20     1-21           580      3.2                                          1-21     1-22           610      3.8                                          1-22     1-23           620      3.6                                          1-23     1-24           580      3.6                                          1-24     1-25           570      2.9                                          1-25     1-26           610      2.0                                          1-26     1-27           590      2.0                                          1-27     1-28           590      1.8                                          1-28     1-29           610      1.8                                          1-29     1-30           570      2.2                                          1-30     1-31           610      2.4                                          1-31     1-32           590      2.4                                          1-32     1-33           580      4.3                                          1-33     1-34           610      2.6                                          1-34     1-35           610      1.8                                          1-35     1-36           600      1.8                                          1-36     1-37           580      2.4                                          1-37     1-38           575      1.7                                          1-38     1-39           590      2.0                                          1-39     1-40           600      2.8                                          1-40     1-41           610      2.5                                          ______________________________________                                    

COMPARATIVE EXAMPLES 1--1 to 1-5

Comparative pigment 1-(1) was prepared.

In place of exemplary disazo pigment 1-(1), an azo pigment having thecoupler structure: ##STR9## was used as comparative pigment 1-(1). Next,in place of exemplary disazo pigments 1-(3), 1-(4), 1-(18) and 1-(20),pigments having the central skeletons of the formulas: ##STR10## wereused, respectively, as comparative pigments 1-(2) to 1-(5).

Comparative pigments ##STR11##

Photosensitive members were prepared in the same manner as that inExample 1--1 except for using comparative pigments 1--1 to 1-5 in placeof the pigment of Example 1--1, and the charging properties weremeasured.

Table 1-2 shows the properties of comparative examples while comparedwith this invention.

                                      TABLE 1-2                                   __________________________________________________________________________                            Com-                                                        Exemplary   E.sub.1/2                                                                           parative                                                                           Comparative E.sub.1/2                            Example*                                                                            pigment No.                                                                          Vo (-V)                                                                            (lux · sec)                                                                example                                                                            pigment No.                                                                          Vo (-V)                                                                            (lux · sec)                 __________________________________________________________________________    1-1   1-1    560  4.0   1-1  1-1    590  7.7                                  1-3   1-3    580  2.9   1-2  1-2    570  15.2                                 1-4   1-4    570  3.0   1-3  1-3    580  8.2                                   1-17  1-18  600  2.6   1-4  1-4    590  8.8                                   1-19  1-20  570  3.8   1-5  1-5    580  17.2                                 __________________________________________________________________________     *Excerpted from Table 11                                                 

As clear from the results in Table 1-2, the photosensitive member ofthis invention is remarkably improved in the electrophotographicsensitivity in comparison with the cases of using the pigments of thestructure wherein the "H" of >NH of the central skelton is substituted,or the pigments of the structure wherein the coupler structure is a3-hydoxynaphthalenecarboxylic acid anilide type. Examples 1-41 to 1-45,and Comparative Examples 1-6 to 1-10

By use of the photosensitive members used in Examples 1--1, 1-3, 1-4,1-17 and 1-19 and those used in Comparative examples 1--1 to 1-5,fluctuations in potential at light portion and potential at dark portionwere measured during repeated uses by means of an electrophotographiccopying machine equipped with a ⊖ 5.6 kV corona charger, an exposureoptical system, a developer, a transfer charger, an deelectrifyingexposure optical system and a cleaner, in which the photosensitivemember was attached on its cylinder. The copying machine is constitutedsuch that an image is obtained on a transfer paper with driving of thecylinder. By use of this copying machine, the initial potentials atlight portion (V_(L)) and at dark portion (V_(D)) were set at around-100 V and -600 V, respectively, and the potentials at light portion(V_(L)) and at dark portion (V_(D)) after repeated uses of 5000 timeswere measured. The results are shown in Table 1-3.

                  TABLE 1-3                                                       ______________________________________                                        Photo-                                                                        sensitive                  After 5000                                         member       Initial values                                                                              sheet copying                                      No.          V.sub.D (-V)                                                                           V.sub.L (-V)                                                                           V.sub.D (-V)                                                                         V.sub.L (-V)                            ______________________________________                                        Example Example                                                               41      1        600      100    620    120                                   42      3        590      100    630    120                                   43      4        590      110    630    130                                   44      17       600       90    610    110                                   45      19       610      100    620    130                                   Com-    Com-                                                                  parative                                                                              parative                                                              example Example                                                                6      1        600      100    670    170                                    7      2        600      100    680    160                                    8      3        590       90    660    160                                    9      4        600      100    690    180                                   10      5        610      100    700    190                                   ______________________________________                                    

The photosensitive members of this invention were very excellent in thestability of V_(D) and V_(L) even during the repetitive uses.

EXAMPLE 1-46

On the charge generation layer prepared in Example 1--1, a coatingsolution prepared by dissolving 5 g of 2,4,7-trinitro-9-fluorenone and 5g of poly-4,4'-dioxydiphenyl-2,2'-propane carbonate (molecular weight300,000) in 70 ml of tetrahydrofuran was applied to a coated amountafter drying of 10 g/m², followed by drying to form a charge transportlayer.

The electrophotographic photosensitive member thus prepared wassubjected to measurement of charging properties according to the samemethod as in Example 1--1. The charging polarity was made ⊕. The resultsare shown in Table 1-4.

                  TABLE 1-4                                                       ______________________________________                                                   Vo   ⊕ 570 volt                                                           E.sub.1/2 :                                                                        5.0 lux · sec                                        ______________________________________                                    

EXAMPLE 1-47

On the aluminum surface of a polyethylene terephthalate film havingaluminum vapor deposited thereon, a coating of a polyvinyl alcohol witha film thickness of 0.5μ was formed.

Next, on the polyvinyl alcohol layer previously formed, the dispersioncontaining the disazo pigment used in Example 1--1 was applied by aMeyer Bar to a film thickness after drying of 0.5μ, followed by drying,to form a charge generation layer.

Subsequently, a solution of 5 g of a pyrazoline compound of the formula:##STR12## and 5 g of a polyalylate resin (condensed polymer of bisphenolA and terephthalic acid-isophthalic acid) dissolved in 70 ml oftetrahydrofuran was applied on the charge generation layer to a filmthickness after drying of 10μ, followed by drying, to form a chargetransport layer.

The charging characteristics and durability characteristics of thephotosensitive member thus prepared were measured in the same manner asExample 1--1 and Example 1-41. The results are shown in Table 1-5.

                  TABLE 1-5                                                       ______________________________________                                        Vo: -600 V                                                                    E.sub.1/2 : 4.5 lux · sec                                            Durability characteristics:                                                   Initial           After 5000 sheet copying                                    V.sub.D  V.sub.L      V.sub.D   V.sub.L                                       ______________________________________                                        -600 V   -100 V       -620 V    -125 V                                        ______________________________________                                    

From the results shown in Table 1-5, the photosensitive member of thepresent invention has good sensitivity and also good in potentialstability when repeatedly used.

EXAMPLE 1-48

An aluminum plate with a thickness of 100 microns was coated with anaqueous ammoniacal solution of casein, followed by drying, to form asubbing layer with a film thickness of 0.5 microns.

Next, a charge transfer complex compound was formed by dissolving 5 g of2,4,7-trinitro-9-fluorenone and 5 g of a poly-N-vinylcarbazole (numberaverage molecular weight: 300,000) in 70 ml of tetrahydrofuran. Thecharge transfer compound and 1 g of the above exemplary disazo pigmentNo. 1-(17) were added into a solution of 5 g of a polyester resin(Byron: produced by Toyobo) dissolved in 70 ml of tetrahydrofuran to bedispersed therein. The resultant dispersion was applied on the subbinglayer to a film thickness after drying of 12 microns, followed bydrying.

The charging characteristics and durability characteristics of thephotosensitive member thus prepared were measured in the same manner asExample 1-1. The charging polarity was made ⊕. The results are shown inTable 1-6.

                  TABLE 1-6                                                       ______________________________________                                        Vo: ⊕ 560 V                                                               E.sub.1/2 : 5.7 lux · sec                                            Durability characteristics:                                                   Initial         After 5000 sheet copying                                      V.sub.D V.sub.L     V.sub.D   V.sub.L                                         ______________________________________                                        600     100         630       125                                             ______________________________________                                    

EXAMPLE 1-49

On the casein of the aluminum substrate applied with the casein layerused in Example 1-1, the charge transfer layer and the charge generationlayer of Example 1-1 were successively laminated. Thus, a photosensitivemember was prepared in entirely the same manner as Example 1-1 exceptfor the different layer constitution, and subjected to chargingmeasurement in the same manner as Example 1-1. However, the chargingpolarity was made ⊕. The results are shown in Table 1-7.

                  TABLE 1-7                                                       ______________________________________                                                   Vo:  ⊕ 565 V                                                              E.sub.1/2 :                                                                        5.8 lux · sec                                        ______________________________________                                    

EXAMPLE 1-50

On an aluminum cylinder, an aqueous ammoniacal solution of casein(casein 11.2 g, 28% ammonia water 1 g, water 222 ml) was applied by dipcoating, followed by drying, to form a subbing layer with a coatedamount of 1.0 g/m².

Subsequently, 1 part by weight of the above disazo pigment No. 1-(4), 1part by weight of a butyral resin (S-Lec BM-2: produced by SekisuiKagaku K.K.) and 30 parts by weight of isopropyl alcohol were dispersedby means of a ball mill disperser for 4 hours. The resultant dispersionwas applied on the subbing layer previously formed by dip coating,followed by drying, to form a charge generation layer with a thicknessof 0.3 micron.

Then, 1 part by weight of the hydrazone compound used in Example 1-1, 1part by weight of a polysulfone resin (P1700, produced by Union CarbideCo.) and 6 parts by weight of monochlorobenzene were mixed and dissolvedby stirring with a stirrer. The resultant solution was applied on thecharge generation layer by dip coating, followed by drying, to form acharge transport layer with a film thickness of 12 microns.

The photosensitive member thus prepared was subjected to coronadischarging of ⊖5 kV. The surface potential (initial potential Vo) wasmeasured. Further, the surface potential after leaving thephotosensitive member to stand in a dark place for 5 seconds (dark decayV_(K)) was measured. The sensitivity was evaluated by measuring theexposure quantity necessary for decaying the potential V_(K) after darkdecay to 1/2 (E_(1/2) microjoule/cm²). During this measurement,gallium/aluminum/arsenic ternary system semiconductor laser (output: 5mW; oscillation wavelength: 778 nm) was used. The results obtained areas follows.

Vo: -520 volt

V_(K) : 88%

E_(1/2) : 1.5 microjoule/cm².

As the next step, real image forming test was carried out by setting theabove photosensitive member in place of the LBP-CS photosensitive memberon the laser beam printer (LBP-CX produced by Canon), which is anelectrophotographic system printer of the reversal development systemequipped with the same semiconductor laser as mentioned above. Theconditions are as follows:

surface potential after primary charging: ⊖700 V; surface potentialafter image exposure: ⊖150 V (exposure quantity 3 μJ/cm²); transferpotential: ⊕700 V; developer polarity: negative; process speed: 50mm/sec; developing condition (developing bias): ⊖450 V; image exposurescanning system: image scanning; exposure before primary charging: wholeexposure with red light of 50 lux.sec.

Image formation was effected by performing line scanning of laser beamfollowing the letter signals and image signals, whereby good prints ofboth letters and images could be obtained.

EXAMPLES 2-1 TO 2-40

Example 1-1 was repeated except that disazo pigments 2-(1) to 2-(60)were used in place of the disazo pigment No. 1-(1) to preparecorresponding photosensitive members.

The surface potential (V_(O)) and exposure quantity (E_(1/2)) of thephotosensitive members were measured in the same manner as Example 1-1to obtain the results shown in Table 2-1.

                  TABLE 2-1                                                       ______________________________________                                                 Exemplary disazo                                                     Example  pigment No.    Vo (-V)  E.sub.1/2  (l · s)                  ______________________________________                                        2-1      2-(1)          570      4.0                                          2-2      2-(2)          610      3.2                                          2-3      2-(3)          590      2.9                                          2-4      2-(4)          580      1.0                                          2-5      2-(5)          610      2.6                                          2-6      2-(6)          590      2.8                                          2-7      2-(7)          610      2.4                                          2-8      2-(8)          600      3.3                                          2-9      2-(9)          610      2.6                                          2-10     2-(10)         620      2.6                                          2-11     2-(11)         610      2.7                                          2-12     2-(13)         600      2.9                                          2-13     2-(16)         600      4.3                                          2-14     2-(20)         590      4.1                                          2-15     2-(21)         580      3.2                                          2-16     2-(22)         580      2.9                                          2-17     2-(28)         610      2.6                                          2-18     2-(29)         600      2.4                                          2-19     2-(32)         580      3.8                                          2-20     2-(35)         590      3.2                                          2-21     2-(38)         600      3.8                                          2-22     2-(40)         610      3.6                                          2-23     2-(41)         590      3.6                                          2-24     2-(44)         580      2.9                                          2-25     2-(45)         600      2.0                                          2-26     2-(46)         600      1.0                                          2-27     2-(47)         600      1.8                                          2-28     2-(48)         590      1.8                                          2-29     2-(49)         580      2.2                                          2-30     2-(50)         600      2.4                                          2-31     2-(52)         600      2.4                                          2-32     2-(54)         590      4.3                                          2-33     2-(57)         600      2.6                                          2-34     2-(58)         610      2.3                                          2-35     2-(59)         600      2.0                                          2-36     2-(64)         590      2.4                                          2-37     2-(51)         585      1.7                                          2-38     2-(53)         600      2.0                                          2-39     2-(55)         610      2.8                                          2-40     2-(60)         610      2.5                                          ______________________________________                                    

COMPARATIVE EXAMPLES 2-1 TO 2-2

Example 2-1 was repeated except that comparative disazo pigments 2-1 and2-2 were used in place of the disazo pigment No. 2-(1) according to thepresent invention to prepare corresponding photosensitive members toprovide Comparative sample 2-1 and Comparative sample 2-2.

Electrophotographic characteristics were evaluated in the same manner asExample 2-1 to obtain the results shown in Table 2-2.

                                      TABLE 2-2                                   __________________________________________________________________________                                                E.sub.1/2                                Structural formula              V.sub.0 (-V)                                                                       (l · s)                  __________________________________________________________________________    Comparative example 2-1                                                               ##STR13##                      580  7.9                               Comparative example 2-2                                                               ##STR14##                      520  13.2                              Example 2-1                                                                           ##STR15##                      570  4.0                               Example 2-2                                                                           ##STR16##                      600  3.3                               __________________________________________________________________________

From Table 2-2, it can be seen that the pigment of thenon-3-hydroxy-naphthalenecarboxylic acid anilide type coupler accordingto the present invention has very excellent electrophotographiccharacteristics.

EXAMPLES 2-41 TO 2-45

By use of the photosensitive members used in Examples 2-1, 2-3, 2-4,2-17 and 2-19, fluctuations in potential at light portion and potentialat dark portion during repeated uses were measured in the same manner asin Example 1-41. The results are shown in Table 2-3.

                  TABLE 2-3                                                       ______________________________________                                        Photo-                     After 5000 sheet                                   sensitive    Initial values                                                                              copying                                            member       V.sub.D (-V)                                                                           V.sub.L (-V)                                                                           V.sub.D (-V)                                                                         V.sub.L (-V)                            ______________________________________                                        Example                                                                              Example                                                                2-41   2-1       600      100    625    120                                   2-42   2-3       590      100    630    120                                   2-43   2-4       590      110    620    130                                   2-44    2-17     600       90    630    110                                   2-45    2-19     610      100    630    130                                   ______________________________________                                    

EXAMPLE 2-46

On the charge generation layer prepared in Example 2-1, a chargetransport layer was formed in the same manner as in Example 1-46.

The electrophotographic photosensitive member thus prepared wassubjected to measurement of charging characteristics according to thesame method as in Example 1-1. The charging polarity was made ⊕. Theresults are shown in Table 2-4.

                  TABLE 2-4                                                       ______________________________________                                                   Vo   ⊕ 550 volt                                                           E.sub.1/2 :                                                                        5.0 lux · sec                                        ______________________________________                                    

EXAMPLE 2-47

The procedure of Example 1-47 was repeated except for using disazopigment 2-(1) in place of pigment No. 1-(1) to prepare a photosensitivemember.

The charging characteristics and durability characteristics of thephotosensitive member thus prepared were measured in the same manner asExample 1-1 and Example 1-41. The results are shown in Table 2-5.

                  TABLE 2-5                                                       ______________________________________                                        Vo: -590 V                                                                    E.sub.1/2  4.0 lux · sec                                             Durability characteristics:                                                   Initial           After 5000 sheet copying                                    V.sub.D  V.sub.L      V.sub.D   V.sub.L                                       ______________________________________                                        -600 V   -100 V       -620 V    -120 V                                        ______________________________________                                    

From the results shown in Table 2-5, the photosensitive member of thepresent invention has good sensitivity and also good in potentialstability when repeatedly used.

EXAMPLE 2-48

Example 1-48 was repeated except for using disazo pigment 2-(26) inplace of pigment 1-(17) to prepare a photosensitive member.

The charging characteristics and durability characteristics of thephotosensitive member thus prepared were measured in the same manner asExample 1-1. The results are shown in Table 2-6.

                  TABLE 2-6                                                       ______________________________________                                        Vo: ⊕ 550 V                                                               E.sub.1/2 : 6.0 lux · sec                                            Durability characteristics:                                                   Initial         After 5000 sheet copying                                      V.sub.D V.sub.L     V.sub.D   V.sub.L                                         ______________________________________                                        +600    +90         +580      +150                                            ______________________________________                                    

EXAMPLE 2-49

On the casein layer of the aluminum substrate applied with the caseinlayer used in Example 2-1, the charge transport layer and the chargegeneration layer of Example 2-1 were successively laminated. Thus, aphotosensitive member was prepared in entirely the same manner asExample 2-1 except for the different layer constitution, and subjectedto charging measurement in the same manner as Example 2-1. However, thecharging polarity was made ⊕. The results are shown in Table 2-7.

                  TABLE 2-7                                                       ______________________________________                                                   Vo:  ⊕ 550 V                                                              E.sub.1/2 :                                                                        5.0 lux · sec                                        ______________________________________                                    

EXAMPLE 2-50

The procedure of Example 1-50 was repeated except for using disazopigment 2-(4) in place of pigment No. 1-(4) to prepare a photosensitivemember.

The potential V_(K) and exposure quantity E_(1/2) of the photosensitivemember thus prepared were measured in the same manner as in Example1-50. The results obtained are as follows.

Vo: -540 volt

V_(K) : 93%

E_(1/2) : 1.2 microjoule/cm².

What we claim is:
 1. An electrophotographic photosensitive member comprising a photosensitive layer on a substrate, said photosensitive layer comprising a disazo pigment represented by the formula: ##STR17## wherein R₁, R₁ ', R₂ and R₂ ' represent hydrogen, halogen, nitro, cyano, or alkyl, aralkyl, alkoxy or aryl group which may have a substituent, A represents a coupler residue having a phenolic OH group, and B represents hydrogen or nitroso group, said A being selected from the formulas (2) to (8) shown below: ##STR18## wherein X represents a residue to be fused with a benzene ring to form a polycyclic aromatic ring of anthracene ring, or a heterocyclic ring; R₃ and R₄ represent hydrogen, alkyl, aralkyl, aryl or heterocyclic ring which may have a substituent, or taken together represent a residue to form a cyclic amino group together with nitrogen atom; R₅ and R₆ each represent alkyl, aralkyl, aryl which may have a substituent; Y represents a divalent aromatic hydrocarbon group or forms a divalent heterocyclic group together with nitrogen atom; Z represents a residue to be fused with a benzene ring to form a polycyclic aromatic ring or heterocyclic ring; R₇ and R₈ represent hydrogen, aryl or heterocyclic group which may have substituent or a residue which forms a 5- to 6-membered ring together with the center carbon atom, which 5- to 6-membered ring may have a fused aromatic ring; R₉ and R₁₀ represent hydrogen, alkyl, aralkyl, aryl or heterocyclic group which may have a substituent.
 2. An electrophotographic photosensitive member according to claim 1, wherein the above photosensitive member is a function separation type comprising a charge generation layer and a charge transport layer, said charge generation layer containing the disazo pigment represented by the above formula (1).
 3. An electrophotographic photosensitive member according to claim 2, wherein the charge transport layer is laminated on the charge generation layer.
 4. An electrophotographic photosensitive member according to claim 2, wherein the charge generation layer is laminated on the charge transport layer.
 5. An electrophotographic photosensitive member according to claim 2, wherein a charge transportatable compound selected from hydrazones, pyrazolines and fluorenones is contained in the charge transport layer.
 6. An electrophotographic photosensitive member according to claim 1, wherein R₃ in the above formula (2) is hydrogen and R₄ is a substituted phenyl represented by the formula: ##STR19## wherein R₁₁ is a substituent selected from halogen, nitro, cyano, and trifluoromethyl group.
 7. An electrophotographic photosensitive member according to claim 1, wherein A in the above formula (1) is represented by the formula (9): ##STR20## wherein R₁₂ represents a phenyl group which may have a substituent.
 8. An electrophotographic photosensitive member according to claim 1, wherein B in formula (1) is hydrogen. 